Synthesis of high density of WS₂ monolayers using chemical vapor deposition method

Tungsten disulfide (WS₂) monolayers are two-dimensional (2D) materials with distinctive characteristics such as large surface area, unique electronic properties, and high charge-carrier transport. These unique characteristics make them promising candidates for use in sensors, catalysis, and energy storage. A reliable and scalable method of synthesizing 2D-WS₂ is desirable to realize their applications. Although there are several prior studies on preparing 2D-WS₂, there is still a lack of reliable methods of preparing high-quality WS₂ monolayers with uniform thickness. In this study, we employ the chemical vapor deposition (CVD) method to grow 2D-WS₂ on Al₂O₂ (0001) substrate utilizing WO₃ and sulfur. We show that the regulated sulfur precursor flow and annealing temperature of WO₃ are crucial for achieving uniform 2D-WS₂ thickness. Our unique experimental setup allows us to precisely control the flow of the sulfur source, resulting in a high proportion of WS₂ monolayers while annealing WO₃ at 850^oC. The atomic force microscopy investigation shows a high density of triangular 2D-WS₂. These triangular WS₂ monolayers exhibit a relatively small lateral size, measuring less than 500 nm. Due to their high edge-site density, these sub-500 nm 2D-WS₂ layers could be ideal for photocatalysis applications.